A3Ti5NbO14 (A = H, Li and K) family: ionic exchange, physical and electrochemical properties

A new layered titanoniobate, Li3Ti5NbO14, a member of the AxM2nO4n+2 family, has been synthesized using a molten salt reaction between H3Ti5NbO14 and an eutectic mixture of LiOH and LiNO3. This compound crystallizes in the P21/m space group with a = 9.273(15) Å, b = 3.788(6) Å, c = 8.871(3) Å, and β = 114.33(1)°, as determined by 3D electron diffraction single crystal analysis. It exhibits [Ti5NbO14]3- layers similar to K3Ti5NbO14, but differs from the latter by a 'parallel configuration' of its [Ti5NbO5]3- ribbons between the two successive layers. The topotactic character of the reaction suggests that exfoliation plays a prominent role in the synthesis of this new form. This new phase intercalates reversibly 2 lithium through a first-order transformation leading to a capacity of 100 mA h g-1 at a potential of 1.67 V vs. Li/Li+.

Zero-Strain Sodium Lanthanum Titanate Perovskite Embedded in Flexible Carbon Fibers as a Long-Span Anode for Lithium-Ion Batteries

"High-capacity" graphite and "zero-strain" spinel Li4Ti5O12 (LTO) occupy the majority market of anode materials for Li+ storage in commercial applications. Nevertheless, their intrinsic drawbacks including the unsafe potential of graphite and unsatisfactory capacity of LTO limit the further development of lithium-ion batteries (LIBs), which is unable to satisfy the ever-increasing demands. Here, a novel Na0.35La0.55TiO3 perovskite embedded in multichannel carbon fibers (NLTO-NF) is rationally designed and synthesized through an electrospinning method. It not only has the advantages of a respectable specific capacity of 265 mAh g-1 at 0.1 A g-1 and superb rate capability, but it also possesses the zero-strain characteristic. Impressively, an ultralong cycling life with 96.3% capacity retention after 9000 cycles at 2 A g-1 is achieved in the half cell, and 90.3% of capacity retention ratio is obtained after even 2500 cycles at 1 A g-1 in the coupled LiFePO4/NLTO-NF full cell. This study introduces a new member with excellent performance to the zero-strain materials family for next-generation LIBs.

Adsorption and Separation of Ethyl Mercaptan from Methane by Hydroxyl Groups on the Surface of HTiNbO5-Nanosheets

Adsorption and separation of light mercaptan (R-SH, R = C₁-C₄) from methane gas can effectively improve the utilization efficiency of methane and the resource conversion of organic sulfide. To further investigate the effects of composition and structural characteristics of laminates on desulfurization performance, in this paper, a two-dimensional (2D) HTiNbO₅-nanosheet (HTiNbO₅-NS) was constructed. In addition, the hydrogen-bonding interaction between the exposed hydroxyl active sites on the surface of HTiNbO₅-NS and ethyl mercaptan (Et-SH) was constructed to realize the adsorption and separation of Et-SH from methane gas. The breakthrough adsorption capacity (C_ap (BT)) of HTiNbO₅-NS is 14.35 mg·g^-1 in a micro fixed bed with a space velocity of 6000 h^-1. The regeneration desulfurization rate (q) of the 10-cycle regeneration adsorption was ca. 96%. Furthermore, density functional theory (DFT) calculation results show that the S atoms of Et-SH and HTiNbO₅-NS with the terminal hydroxyl and bridge hydroxyl have electron cloud covering to form the hydrogen-bonding interaction. In addition, the formation details of this hydrogen-bond interaction are discussed. The effects of Ti on the microstructure, hydroxyl acid, hydroxyl content, surface area, and pore volume of nanosheets were studied to explain the reasons for the differences in the properties of the two kinds of nanosheets. This work broadens the design of 2D niobium-based efficient adsorbents for R-SH based on hydrogen-bonding interaction and is helpful to enrich the application of the hydrogen-bonding interaction.

Ti-Based Oxide Anode Materials for Advanced Electrochemical Energy Storage: Lithium/Sodium Ion Batteries and Hybrid Pseudocapacitors

Titanium-based oxides including TiO₂ and M-Ti-O compounds (M = Li, Nb, Na, etc.) family, exhibit advantageous structural dynamics (2D ion diffusion path, open and stable structure for ion accommodations) for practical applications in energy storage systems, such as lithium-ion batteries, sodium-ion batteries, and hybrid pseudocapacitors. Further, Ti-based oxides show high operating voltage relative to the deposition of alkali metal, ensuring full safety by avoiding the formation of lithium and sodium dendrites. On the other hand, high working potential prevents the decomposition of electrolyte, delivering excellent rate capability through the unique pseudocapacitive kinetics. Nevertheless, the intrinsic poor electrical conductivity and reaction dynamics limit further applications in energy storage devices. Recently, various work and in-depth understanding on the morphologies control, surface engineering, bulk-phase doping of Ti-based oxides, have been promoted to overcome these issues. Inspired by that, in this review, the authors summarize the fundamental issues, challenges and advances of Ti-based oxides in the applications of advanced electrochemical energy storage. Particularly, the authors focus on the progresses on the working mechanism and device applications from lithium-ion batteries to sodium-ion batteries, and then the hybrid pseudocapacitors. In addition, future perspectives for fundamental research and practical applications are discussed.

Oxygen Reduction Behavior of HDH TiH2 Powder during Dehydrogenation Reaction

In this study, oxygen reduction behavior of TiH2 powders during dehydrogenation process was investigated based on thermodynamics. During the hydrogenation–dehydrogenation (HDH) method to fabricate Ti powder, TiH2 was formed from a Ti sponge through hydrogenation annealing, and was easily pulverized even by ball milling due to its brittle nature. The ball milling process caused an increase in the oxygen concentration from 0.133 to 0.282 wt %, and transmission electron microscopy and X-ray photoelectron Spectroscopy results demonstrated that the formation of oxide layers such as TiO and TiO2 formed on the surface of the TiH2 powder resulted in the higher oxygen content. Dehydrogenation, which is the process originally conducted to eliminate hydrogen from TiH2, was used to remove and/or reduce oxygen, resulting in the reduction of the oxygen concentration from 0.282 to 0.216 wt %. Thermodynamic calculations confirmed the possibility of oxygen reduction by atomic hydrogen but molecular hydrogen has no function for the oxygen reduction. Glow discharge mass spectrometry (GD-MS) analysis, which checks H2O flow as an evidence of the oxygen reduction by hydrogen, supported the fact that the atomic hydrogen formed during the dehydrogenation process is able to play a critical role in decreasing the oxygen content.

H0.92K0.08TiNbO5 Nanowires Enabling High-Performance Lithium-Ion Uptake

HTiNbO₅ has been widely investigated in many fields because of its distinctive properties such as good redox activity, high photocatalytic activity, and environmental benignancy. Here, this work reports the synthesis of one-dimensional H_0.92K_0.08TiNbO₅ nanowires via simple electrospinning followed by an ion-exchange reaction. The H_0.92K_0.08TiNbO₅ nanowires consist of many small "lumps" with a uniform diameter distribution of around 150 nm. Used as an anode for lithium-ion batteries, H_0.92K_0.08TiNbO₅ nanowires exhibit high capacity, fast electrochemical kinetics, and high performance of lithium-ion uptake. A capacity of 144.1 mA h g^-1 can be carried by H_0.92K_0.08TiNbO₅ nanowires at 0.5 C in the initial charge, and even after 150 cycles, the reversible capacity can remain at 123.7 mA h g^-1 with an excellent capacity retention of 85.84%. For H_0.92K_0.08TiNbO₅ nanowires, the diffusion coefficient of lithium ions is 1.97 × 10^-11 cm² s^-1, which promotes the lithium-ion uptake effectively. The outstanding electrochemical performance is ascribed to its morphology and the formation of a stable phase during cycling. In addition, the in situ X-ray diffraction and ex situ transmission electron microscopy techniques are applied to reveal its lithium storage mechanism, which proves the structure stability and electrochemical reversibility, thus achieving high-performance lithium-ion uptake. All these advantages demonstrate that H_0.92K_0.08TiNbO₅ nanowires can be a possible alternative anode material for rechargeable batteries.

All-carbon-based porous topological semimetal for Li-ion battery anode material

Topological state of matter and lithium batteries are currently two hot topics in science and technology. Here we combine these two by exploring the possibility of using all-carbon-based porous topological semimetal for lithium battery anode material. Based on density-functional theory and the cluster-expansion method, we find that the recently identified topological semimetal bco-C₁₆ is a promising anode material with higher specific capacity (Li-C₄) than that of the commonly used graphite anode (Li-C₆), and Li ions in bco-C₁₆ exhibit a remarkable one-dimensional (1D) migration feature, and the ion diffusion channels are robust against the compressive and tensile strains during charging/discharging. Moreover, the energy barrier decreases with increasing Li insertion and can reach 0.019 eV at high Li ion concentration; the average voltage is as low as 0.23 V, and the volume change during the operation is comparable to that of graphite. These intriguing theoretical findings would stimulate experimental work on topological carbon materials.

Bimolecular-induced hierarchical nanoporous LiTi2(PO4)3/C with superior high-rate and cycling performance

Carbon-coated hierarchical LiTi₂(PO₄)₃ was synthesized by a facile bimolecular (glucose and DMEA) assisted hydrothermal reaction and a solid-state reaction, and exhibits excellent high-rate and cycling performance.